The proliferation of fungal hyphae in soils supporting mycorrhizal and non-mycorrhizal plants

This study investigated the impact of mycorrhizal plants, non-mycorrhizal plants and soil organic matter on the relative abundance of soil hyphae perceived to belong to indigenous arbuscular mycorrhizal (AM) plants. The mycorrhizal plants corn (Zea mays L.) and barley (Hordeum vulgare L.) and a non-mycorrhizal plant, canola (Brassica napus L.), were grown in unsterilized soil in pots inoculated with mycorrhizal corn root fragments. The abundance of hyphae was measured after 5 weeks and the response of fungal growth to the addition of corn residues in the absence of plants was assessed. The abundance of hyphae was higher in the presence of the mycorrhizal plants than in the other treatments. AM hyphae present under mycorrhizal plants accounted for more than 83% of the measured hyphae. The levels of root colonization of 32% in corn and 27% in barley confirmed the mycorrhizal status of the experimental plants. Only a few points of entry were observed in canola, the non-host plant. The percentage of mycorrhizal colonization was positively related (R ²?=?0.85) to the abundance of soil hyphae, indicating that AM hyphae were the major component of the soil hyphae in the presence of mycorrhizal plants in this study.     

Luteolytic influence of intrauterine dead embryos in the early pregnant rat

The present investigation was an endeavour to study if annihilation of embryos in the uterus of the rat before the establishment of placental luteotropic functions has any influence on corpus luteal function, and, if there is any, whether it is local or systemic. The responsibility of pregnancy maintenance was imposed on a single ovary by performing unilateral ovariectomy after implantation (on Day 5 postcoitum). The implantation sites in one uterine horn, either ipsilateral or contralateral to the remaining ovary, were selectively destroyed by injecting 0.1 ml of sterile normal saline to that particular horn only, and the peripheral progesterone level and viability of the embryos in the untreated horn, which depended on the functions of the remaining ovary, were examined. Selective killing of embryos in the uterine horn of the ovariectomized side did not exert any influence on the fetal viability in the untreated horn ( nonovariectomized side) and the peripheral progesterone level also remained statistically unaffected. On the contrary, induction of fetal resorptions in the uterine horn of the intact side produced a significant fall in the peripheral level of progesterone and induced resorption of embryos of the ovariectomized side also. The latter could significantly be prevented by simultaneous administration of exogenous progesterone, indicating luteolysis as the major, if not sole, factor responsible for fetal resorption in the untreated horn. The luteolytic effect was attributed neither to saline itself, nor to the distension of the uterine horn caused by saline injection. Luteolytic factors from the dead embryo-bearing horn which act locally on the adjacent ovary only, are discussed.     

Bacterial overgrowth by indigenous microflora in the phytohemagglutinin-fed rat

Phytohemagglutinin lectin (PHA) derived from red kidney bean (Phaseolus vulgaris) causes bacterial and protozoal colonization of the rat small intestine. To provide additional insights into this phenomenon we have studied the time course and population dynamics of microbial colonization of the major aerobe--facultative anaerobe groups which characterize this microflora. Compared with controls, PHA caused proliferation of a consistent adherent microbial flora in the jejunum (P less than 0.01). The predominant bacteria identified were Escherichia coli. a Streptococcal sp., and Lactobacillus. Escherichia coli isolates expressed no predominant serotype or fimbriae; none elaborated heat-labile or heat-stable toxin. Both E. coli and Streptococcal sp. populations increased within 24 h of PHA feeding and were sustained during further exposure to PHA (P less than 0.05). On reversion to a control diet, coliform counts fell progressively within 24-48 h and continued to decline, whereas gram-positive rod and coccus flora became the more prominent colonizers through days 1 to 4 of the reversion.     

Carbon-hydrogen bond activation of phenyldi(2-thienyl)phosphine at a triosmium cluster centre

The phenyldi(2-thienyl)phosphine (PhPTh₂) complexes [Os₃(CO)_12−n(PhPTh₂)_n] (n = 1-3) (1-3) have been prepared. Thermolysis of 1 and either 2 or 3 in octane affords carbon-hydrogen bond activation products [Os₃(CO)₉{μ₃-PPhTh(C₄H₂S)}(μ-H)] (4) and [Os₃(CO)₈(PPhTh₂){μ₃-PPhTh(C₄H₂S)}(μ-H)] (5), respectively. Both exist as isomeric mixtures differing in the relative positions of phenyl and thienyl substituents with respect to the triosmium centre. The nature of the process has been confirmed by a single crystal X-ray diffraction analysis of 4.     

Effect of pelvic endometrial implants on overall reproductive functions of female rats

The effects of pelvic endometrial implants on the overall reproductive potential of female rats were investigated. After homologous transplantation in the peritoneum, the ectopic endometrium developed into highly vascularized nodes that gradually increased in mass until the 9th week postsurgery and then plateaued. In the presence of these implants, overall reproductive function was adversely affected. The effect was of greatest magnitude during 50-70 days posttransplantation. As compared with values in corresponding controls, ovulation was reduced by 43% (6 of 14) (p < 0.05), mating rate was reduced by 44% (12 of 27) (p < 0.025), and premature termination of pregnancy occurred in 34% (5 of 15) of rats. Wastage of pregnancy, which included complete termination or reduction of fetal number, occurred during the postimplantation course of gestation. Furthermore, 100% of the rats with transplants failed to respond to the copulomimetic stimulation for the induction of pseudopregnancy (p < 0.01, compared with corresponding controls). However, on exposure to vasectomized males, 46% (6 of 13) of these rats exhibited development of pseudopregnancy (p < 0.05, compared with corresponding group receiving copulomimetic stimulation). Increased rate of mating failure and differential pseudopregnancy rates after copulomimetic and natural cervical stimulation suggest that the rats with endometrial explants possibly had an absence or a short appearance of behavioral estrus. Hormonal assessment during the preovulatory phase showed a tendency toward lower mean levels of preovulatory estradiol and significantly lower LH (p < 0.01) and progesterone (p < 0.01) concentrations. The adversely affected reproductive functions may be a secondary consequence of these altered endocrine milieus.     

Fermentation characteristics and protein expression patterns in a recombinant Escherichia coli mutant lacking phosphoglucose isomerase for poly(3-hydroxybutyrate) production

For the efficient production of poly(3-hydroxybutyrate) (PHB) using recombinant Escherichia coli, it is of primal importance to overproduce NADPH, which is necessary for the PHB synthetic pathway. In order to overproduce NADPH in the pentose phosphate (PP) pathway, a recombinant E. coli was constructed in which the phosphoglucose isomerase ( pgi) gene was knocked out to force the carbon flow into the PP pathway. The fermentation characteristics of the recombinant E. coli mutant lacking pgi were then investigated to determine the effect of overproduction of NADPH on efficient PHB production. It was found that, compared with the parent strain ( E. coli JM109), growth of the E. coli mutant lacking pgi ( E. coli DF11) is repressed due to NADPH overproduction in the PP pathway. Furthermore, repressed cell growth can be recovered to some extent by introducing a NADPH-consuming pathway, such as the PHB synthetic pathway. Efficient PHB production using such recombinant E. coli (DF11/pAeKG1) could be attained by appropriately controlling the glucose concentration in the fermentor. Total gene expression was investigated at the protein level by two-dimensional electrophoresis. Out of 22 differentially expressed proteins, 12 were identified with the aid of MALDI-TOF mass spectrometry. Variations in the accumulation of PHB in the recombinant pgi mutant carrying phb (E. coli DF11/pAeKG1) corresponded to the expression of proteins encoded by rpsA, znuA, fabD, potD, fkpA, gapA, ynaF and ibpA. The unfavorable conditions generated by PHB accumulation in the pgi mutant carrying phb resulted in the highest expression of 30S ribosomal protein S1, which ultimately caused a further increase in soluble protein synthesis.     

Vertical distribution of arbuscular mycorrhizal fungi under corn (Zea mays L.) in no-till and conventional tillage systems

 We compared the vertical distribution (0–25 cm) of arbuscular mycorrhizae, extraradical hyphae, and glomalean spores at grain-filling of corn under conventional tillage versus no tillage. Root colonization, total hyphae density, and spore density were correlated, and were highest at a depth of 0–15 cm in soil. Tillage significantly reduced total hypha density and spore density at 0–5 cm depth, but did not affect root colonization. Plowing below 15 cm is likely to diminish AM fungus inocula in the rooting zone of establishing seedlings. Accepted: 19 April 1998     

Miticide bioassays with spider mites (Acari: Tetranychidae): effect of test method,exposure period and mortality criterion on the precision of response estimates

Six different bioassay methods were evaluated using propargite (Omite 30% wettable powder (WP) and fenbutatin oxide (Torque 50% (WP) and 55% suspension concentrate (SC)) with twospotted spider mite, Tetranychus uriticae Koch (TSM) and European red mite, Panonychus ulmi Koch (ERM) to document their utility and precision for estimating median lethal concentrations (LC). For each method, two post-treatment exposure periods and mortality criteria were used. Post-treatment exposure period and mortality criterion had a significant influence on the precision of LC₅₀ estimates for all tested miticides with all bioassays methods. Twenty four hour (h) post-treatment exposure was found to be the most suitable for the slide dip and Petri dish methods while 48h was the most appropriate for leaf disc methods. Scoring moribund mites as dead was the most satisfactory criterion for ensuring that biossays were as simple and precise as possible. The Petri dish residue-Potter tower method (PDR-PT) estimated the responses of TSM and ERM to propargite with high precision. The same method was not as precise for fenbutatin oxide formulations. Because significant mite run-off occurred with the leaf disc methods, their precision was not fully established. The slide dip method gave less precise estimates of LC₅₀ values for propargite (WP) and fenbutatin oxide (WP), while the same method gave more precise LC₅₀ estimates for fenbutatin oxide (SC) than the PDR-PT method. The toxicity of candidate miticides was found to be method-and species-dependent.